An acidic fog in pasadena was found to have a ph of 2.50. which expression represents this ph measurement?

Supposing a temperature of 25 degrees and supposing that all activity coefficients are 1 

pH = -log[H+] 
pOH = -log[OH-] 
pH + pOH = 14 

Thus a pH of 2.50 would mean that the [H+], the concentration of the hydrogen ion, would be 10^(-2.50) 

pH + pOH = 14 
pOH = 14 - pH = 14 - 2.5 = 11.5 
MOH- levels would be coordinated with pOH 
pOH = -log[OH-] ==> [OH-] = [MOH-] = 10^-pOH = 10^-11.5 = 3.2 x 10^-12 

Therefore, MOH¯ = 3.2 × 10¯12 M 

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.

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